480 A FISH-EATING RAT CHAR pads, a state of affairs which characterises a number of these Bodents. The genera Megalomys, Chilomys, HeitTirodontomys, Eligmo- dontia, Nectomys, Rhipidomys, Tylomys, Uolochilus, Heithrodon, Phyttotis, Scapteromys, Acodon, Oxymycterus, Ichthyomys, Blari- nomys, Notiomys are South American forms. Oryzomys and Mheitkrodontomys are common to both parts of the Kew "World. The genus IcJithyomys is remarkable on account of its un~ B-odent-like habits and of certain associated structural changes. I. stolzmanni was obtained from Mount Chanchamays in Peru. at an altitude of 3000 feet; it is a habitual fish-eater, and lives in streams. Another species, I. Jiydrobates, was formerly referred to Habrothrix. The skull shows likenesses to that of the Australian Hydromys; but the most marked characters of adaptation are those of the teeth and caecum. The cutting edges of the upper incisors form a reversed V of obvious use in holding a slippery fish. The caecum is much reduced, short, and narrow. The general Otter-like shape of the creature is largely due to its flattened head, though its " size and general proportions are much as in the common Black B-at." * This sub-family contains a number of genera from Madagascar, viz. Br achy tarsomys, JWeso-mys, HallomySj Bra£hyuromys> jETypo- geo-mys, Grym'nuroTnys, and lEliurus. Sub-Fam. 10. Heotominae.—The last sub-family of the Muridae is that of the Neotominae, containing the ^NTorth Ameri- can genera NeQtom,a> ^Keno'nvys, Hodomys, and JVelsonia. Fam. 3. Bathyergidae.—This family contains several genera which consist of subterranean forms. All these Kodents agree in a number of characters, of which the principal are as follows:— The eyes are very small, and the external ears are reduced to the merest fringe of skin round the aural aperture. The legs are short, as is the tail; the hair-covering is reduced—a reduction which finds its culmination in the nearly nude IleterocepTiatus. Being burrowing creatures, a number of other modifications in accordance with this mode of life are to be seen in their structure. The upper incisors stand out in front of the closed lips, and prevent the entrance of earth. For the same reason 1 See O. Thomas, "On some Mammals from Central Peru," Proc. Zool* Soo.